Seasonal nitrate physiology of Macrocystis integrifolia Bory

Ambient sea-water nitrate and tissue nitrogen (ethanol soluble nitrate and amino acids, as well as total nitrogen) of Macrocystis integrifolia Bory were monitored over a 2-yr period in Bamfield, Vancouver Island, British Columbia. Sea-water nitrate varied from a high of 12 μmol · 1^?1 (individual values as high as 23 μmol · 1^?1 were recorded) in late winter to below detection limits for most of the summer. Tissue nitrate and total nitrogen paralleled the ambient nitrate levels and showed summer minima and winter maxima (from 0 to 70 μmol · g fresh wt^?1 for nitrate and from 0.8 to 2.9% of dry wt for total N). The nitrate uptake capacity was inversely proportional to tissue nitrate concentration and, furthermore, was much higher for subapical surface blades (60–70 nmol · cm^?2 · h^?1) than for older, deeper blades (5–10 nmol · cm^?2 · h^?1). Nitrate uptake by subapical blade disks in summer is apparently higher in dark (1.0–1.7 μmol · g fresh wt^?1 · h^?1) than in light (0.6–1.3 μmol · g fresh wt^?1 · h^?1) and the data obtained in 36–108 h experiments indicate nitrate pool sizes of 30–90 μmol · g fresh wt^?1. These pools are $\text{2}\text{3}$ to nearly full in winter. Ammonium does not inhibit nitrate uptake. It is taken up and apparently utilized much faster than nitrate and it may well be an important source of nitrogen for marine macrophytes.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

Relationships between irradiance and photosynthesis for marine benthic green algae (Chlorophyta) of differing morphologies

Photosynthesis-irradiance relationships were determined in the field for five species of littoral and shallow sublittoral marine benthic green algae (Chlorophyta) of differing morphologies. Each species exhibited a linear increase in photosynthetic rate with increasing irradiance up to a maximum light-saturated value. Full sunlight (1405 to 1956 μE·m^?2·s^?1) inhibited photosynthesis of all species except the thick, optically dense, Codium fragile (Sur.) Har. Compensation irradiances ranged from 6.1 μE·m^?2·s^?1 for Enteromorpha intestinalis (L.) Link to 11.4 μE·m^?2·s^?1 for Ulva lobata (Kütz) S. & G. and did not reveal a consistent relationship to seaweed morphology. Saturation irradiances were determined statistically (I_k) and visually from graphical plots. with the latter technique resulting in values three to eight times higher and different comparative rankings of species than the former. I_k saturation irradiances were highest for Chaetomorpha linum (Müll.) Kütz. (81.9 μE·m^?2·s^?1) and lowest for Codium fragile (49.6 μE·m^?2·s^?1) and did not reveal a relationship with seaweed morphology. Regression equations describing light-limited photosynthetic rates and the relative magnitudes of the maximal net photosynthetic responses both strongly suggested a relationship with seaweed morphology. Highest net photosynthetic rates were obtained for the thin, sheet-like algae Ulva lobata (9.2 mg C·g dry wt^?1·h^?1), U. rigida C. Ag. (6.5 mg C·g dry wt^?1·h^?1) and the tubular form, Enteromorpha intestinalis (7.3 mg C·g dry wt^?1·h^?1), while lowest rates occurred for Codium fragile (0.9 mg C·g dry wt^?1·h^?1). Similarly, steepest light-limited slopes were found for the algae of simpler morphology, while the most gradual slope was determined for Codium fragile, the alga with greatest thallus complexity.     

Productivity of theEcklonia cava community in a bay of Izu Peninsula on the Pacific Coast of Japan

Net production of theEcklonia cava community was monitored on a monthly basis for a year, and annual net production was estimated. Growth rate of blades reached a maximum of about 13 g dry wt·m^?2·day^?1 in spring and a minimum of about 2 g dry wt·m^?2·day^?1 in late summer. Annual production of blades was calculated to be 2.84 kg dry wt·m^?2·year^?1. If the growth of stipes is taken into account, annual net production is estimated to be about 2.9 kg dry wt·m^?2·year^?1. Standing crop was monitored monthly for two and a half years, and a close negative correlation was found between seasonal change in standing crop and net production. Standing crop reached a maximum of about 3 kg dry wt·m^?2 in summer and a minimum of about 1 kg dry wt·m^?2 in winter. Low productivity in summer at a period of maximum biomass may be explained by the dense canopy and the large area of reproductive portion occupying a blade, which diminish net assimilation.     

REPRODUCTION AND MORPHOLOGICAL VARIATION IN SOUTHERN CALIFORNIA POPULATIONS OF THE LOWER INTERTIDAL KELP EGREGIA MENZIESII (LAMINARIALES)1

Intertidal Egregia menziesii (Turner) Aresch. populations were studied at three Southern California sites to determine temporal and spatial patterns of reproduction and morphology. The timing of sporophyll production and sporophyte recruitment was similar at all sites. Sporophyll production was much greater during winter periods of colder seawater temperatures and shorter day lengths. Sporophyte recruitment occurred from spring through midsummer, ～5 months following maximal sporophyll production. Lateral blade morphologies varied in a consistent manner, suggesting a developmental mechanism for form variation in Egregia thalli. Spatulate blades dominated shorter axes and the bases of longer axes, whereas filiform laterals became abundant toward the tips of longer axes. Filiform laterals (9.8 mg O₂·g^?1·h^?1) had higher light‐saturated net photosynthetic rates than spatulate laterals (6.8 mg O₂·g^?1·h^?1), resulting in a 12% increase in the productivity of Egregia per meter of filiform frond.     

Ammonia nitrogen and inorganic phosphorus excretion by the planktonic rotifers

Two series of experiments were carried out to determine the relation of the rate of phosphorus and nitrogen excretion by the planktonic rotifers to ambient temperature and individual body weights of these animals. The following formulas describing this relation were obtained: E_P=0.0154 W^?1.27 e^0.096T E_N=0.0879 W^?1.01 e^{0.088 T}, where E_P and E_N denote the rate of P and N excretion, respectively, in µg · mg dry wt^?1 · h^?1, W is body weight in µg dry weight, and T is temperature in °C.     

Studies on nitrate reductase activity in Laminariadigitata (Huds.) Lamour. I. Longitudinal and transverse profiles of nitrate reductase activity within the thallus

The distribution of the enzyme nitrate reductase (NR) within the thallus of the brown alga Laminaria digitata (Huds.) Lamour is described for plants sampled from the east coast of Scotland in May and June when growth rates are at a maximum. Highest NR activities (≈ 0.2 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the mature blade. NR activities declined towards the basal meristematic region of the blade. Activities in the stipe and holdfast were also low, being between 0.05 and 0.07 μmol NO₃^? reduced·g^?1 wet wt·h^?1. The activities of the enzyme glutamine synthetase (GS), which is important in the assimilation of NH₄⁺, showed a similar distribution within the blade to those of NR.The transverse profile of NR activity in the stipe exhibited a decline from the outer to the inner tissues. Maximum activities (0.13 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the meristoderm, while those of the cortex and medulla were 0.04 and 0.01 μmol NO₃^? reduced·g^?1 wet wt·h^?1 respectively.These data indicate that most of the NO₃^? assimilation occurs in the mature blade rather than in the meristematic tissue where there is a high nitrogen demand for growth. The data are consistent with the maintenance of meristematic growth by the internal transport of organic nitrogen from the mature blade.     

PHYSIOLOGICAL INDICATORS OF NUTRIENT DEFICIENCY IN CLADOPHORA (CHLOROPHYTA) IN THE CLARK FORK OF THE COLUMBIA RIVER,MONTANA1

Cellular nutrient concentrations and nutrient uptake rates of Cladophora glomerata (L.) Kuetzing were determined during summer and fall in 1989–1990 at a site on the upper Clark Fork of the Columbia River, Montana. Both physiological tests indicated that Cladophora growth is likely to be limited by nitrogen during late summer-early fall. Maximum uptake rates of ammonia-N and nitrate-N were 5935–6991 and 507–984 μg · g DW^?1· h^?1, respectively, during July–October when dissolved inorganic nitrogen (DIN) concentrations in the river were less than 10 μg · L^?1. During November-December, when DIN was 72–376 μg · L^?1, maximum ammonia-N uptake was 1137–1633 μg · g DW^?1· h^?1 and maximum nitrate-N uptake was 0–196 μg · g DW^?1· h^?1. Cellular nitrogen during summer–early fall was 0.78–1.80% of Cladophora dry weight, frequently at or below 1.1%, a level suggested as a critical minimum N concentration for maximum growth. In contrast, cellular P was 0.18–0.36% of dry weight, 3–6 times the suggested critical P concentration of 0.06%. Molar ratios of cellular N:P (< 16:1) and DIN: SRP (< 4:1) during late summer-early fall also indicated potential N limitation. Cellular N and P from Cladophora collected from a second site influenced by a municipal wastewater discharge in 1990 displayed similar seasonal trends. At both sites, seasonal fluctuations in DIN were closely tracked by changes in cellular N, Cellular P, however, increased through the growing season despite declining levels of SRP in the river.     

MORPHO‐FUNCTIONAL PATTERNS OF PHOTOSYNTHESIS IN THE SOUTH PACIFIC KELP LESSONIA NIGRESCENS: EFFECTS OF UV RADIATION ON 14C FIXATION AND PRIMARY PHOTOCHEMICAL REACTIONS1

The morpho‐functional patterns of photosynthesis, measured as ¹⁴C‐fixation and chl fluorescence of PSII, also as affected by different doses of UV radiation in the laboratory were examined in the South Pacific kelp Lessonia nigrescens Bory of the coast of Valdivia, Chile (40°S). The results indicated the existence of longitudinal thallus profiles in physiological performance. In general, blades exhibited higher rates of carbon fixation and pigmentation as compared with stipes and holdfasts. Light‐independent ¹⁴C fixation (LICF) was high in meristematic zones of the blades (3.5 μmol ¹⁴C·g^?1 fresh weight [FW]·h^?1), representing 2%–16% (percentage ratio) of the photosynthetic ¹⁴C fixation (20 μmol ¹⁴C·g^?1 FW·h^?1). Exposures to UV radiation indicated that biologically effective UV‐B doses (BED_{photoinhibition300}) of 200–400 kJ·m^?2 (corresponding to current daily doses measured in Valdivia on cloudless summer days) inhibit photosynthetic ¹⁴C fixation of blades by 90%, while LICF was reduced by 70%. The percentage ratio of LICF to photosynthetic ¹⁴C fixation increased under UV exposure to 45%. Primary light reactions measured as maximum quantum yield (F_v/F_m) and electron transport rate (ETR) indicated a higher UV susceptibility of blades as compared with stipes and holdfasts: after a 48 h exposure to UV‐B, the decrease in the blades was close to 30%, while in the stipes and holdfasts it was <20%. The existence of translocation of labeled carbon along the blades suggests that growth at the meristem may be powered by nonphotosynthetic processes. A possible functional role of LIFC, such as during reduction of photosynthetic carbon fixation due to enhanced UV radiation, is discussed. These results in general support the idea that the UV‐related responses in Lessonia are integrated in the suite of morpho‐functional adaptations of the alga.     

FATE OF THE TOXIC CYCLIC HEPTAPEPTIDES,THE MICROCYSTINS,FROM BLOOMS OF MICROCYSTIS (CYANOBACTERIA) IN A HYPERTROPHIC LAKE1

The in situ fate of the toxic cyclic heptapeptides, the microcystins, produced by blooms of Microcystis was examined at two stations in a hypertrophic Japanese lake. Microcystins were detected in all samples of Microcystis with quantities varying seasonally and spatially (230–950 μg · g dry wt^?1 at St. 1 and 160–746 μg · g dry wt^?1 at St. 2) and composed of microcystin-LR, -RR, and-YR. Microcystin-RR was the dominant toxin in most samples. A large amount of microcystin (1.1 μg · L^?1) was detected in only one sample of filtered lake water. Accumulation of microcystin in zooplankton was indirectly estimated from a newly developed equation model. Large amounts of microcystin (75–1387 μg · g dry wt^?1) were accumulated in the zooplankton community, which consisted of two cladocerans, Bosmina fatalis Burckhardt and Diaphanosoma brachyurum Lieve, and a copepod, Cyclops vicinus Uljanin, that co-occurred with the toxic Microcystis blooms. The maximum percent of microcystin content in zooplankton to that in Microcystis was 202%. Among the three species of zooplankton, only B. fatalis seemed to be responsible for accumulation of the microcystins because C. vicinus appeared to avoid contact with Microcystis cells and D. brachyurum did not consume colonies of Microcystis. Microcystins may be transferred to higher trophic levels through B. fatalis.     

TRANSLOCATION OF IODINE IN LAMINARIA SACCHARINA(PHAEOPHYTA)1

Long-distance translocation of ¹²⁵I in Laminaria saccharina (L.) Lamour. followed a “source to sink” pattern. When the source of ¹²⁵I was placed on the distal mature part of the blade, the translocation was unidirectional, basipetal and directed towards the meristematic region at the blade-stipe junction. When the source was placed directly at the meristem there was no movement of label distal to the meristem. The velocity of¹²⁵I transport ranged from 2 to 3.5 cm · h^?1. The anion I^? seemed to be the only species of¹²⁵I transported. An assay of iodine content in different parts of L. saccharina plant showed much higher levels of iodine in the meristem, stipe and holdfast than in the blade. This distribution concurs well with the pattern of I^? translocation.     

The effect of food composition on ingestion,development, and survival of a harpacticoid copepod, Tisbe cucumariae Humes

Feeding experiments were carried out on the benthic harpacticoid copepod Tisbe cucumariae Humes, using seven different diets of various dried and ground macroalgae and marsh grass, algal Aufwuchs, diatoms, polychaete meat, and cereal. In short-term experiments (1 h), ¹⁴C-labelled foods were used to measure ingestion rate of non-ovigerous adult females (individual dry wt = 5.57 ± 2.49 μg). No significant difference was found among the rates at which all foods, except polychaete meat, were ingested (12.7 to 17.3 × 10^?2μg dry wt· ind^?1· h^?1). Polychaete meat was consumed faster (23.9 × 10^?2μg dry wt·ind ^?1· h^?1). The nutritional value of the foods was estimated in long-term experiments (22 days) by measuring development time and survival of T. cucumariae. Both these variables were significantly correlated with the nitrogen, protein content, and C:N ratio of the foods. No relation was found, however, with the amount of carbon, calories and available calories in the diets. Thus, nitrogen (protein) content of the food was the factor limiting secondary production of the copepods.     

Pelagic Sargassum community metabolism: Carbon and nitrogen

The production, nitrogen fixation, and release rates and fate of dissolved organic matter of a pelagic Sargassum community have been investigated at eight stations in the Gulf Stream and the Sargasso Sea. Net production and gross nitrogen fixation rates of Sargassum and epiphytes varied significantly between stations, 328 ± 114μg C (g dry wt)^?1h^?1 and 18 ± 7.4μg N g^?1h^?1, respectively. The net release rates of dissolved organic carbon (287 ± 150μg DOC g^?1h^?1) also showed the same variability between stations. On the other hand, the community carbon and nitrogen content, 268 ± 4.8 and 16.9 ± 2.4 mg g dry wt^?1, respectively, remained constant at all stations. The results of chemical measurements indicate that ≈ 0–50 % of the gross production was lost as a result of photosynthate release. From ¹⁴C-tracer experiments it was found that the planktonic and epiphytic heterotrophs mineralized 50–70 % of the photosynthate released by Sargassum and epiphytic algae. Based on the community gross production and fixation rates, carbon and nitrogen content, the amount of nitrogen required for the observed production rates, the Sargassum community appears to obtain a substantial part (40%) of its nitrogen from nitrogen fixation.     

SEASONAL PHOTOSYNTHETIC PERFORMANCE OF MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1

The seasonal photosynthetic performances of three age classes of blades of Macrocystis integrifolia Bory were estimated by studying their photosynthetic rate vs. irradiance curves and pigment contents for 15 months. All blade types were irradiance-saturated between 25 and 70 μE · m^?2· S^?1. Young and mature blade tissues had higher photosynthetic maxima and initial slopes on an area basis than older blade tissue. The latter, however, had pigment concentrations similar to those in mature blade tissues. All these parameters varied on a seasonal basis. The photosynthetic maxima ranged from 0.1–0.8 μmol · C · cm^?2· h^?t and showed two peaks, one in late summer-early fall and the other in late winter. Changes in initial slope and pigment concentrations in the blade tissues suggest that, changes in the size or efficiency of electron transfer in the photosynthetic unit occur. These data are discussed in relation to changes in seawater temperature and nitrate concentrations.     

Optimization of gluconic acid synthesis by removing limitations and inhibitions

The optimization task was performed using the gluconic acid synthesis by the Acetobacter methanolicusMB 58 strain. The microorganisms were grown continuously on methanol as the growth substrate. After finishing the growth process by the deficiency of N and P, the gluconic acid synthesis was started by adding glucose. The synthesis process was performed continuously. The oxygen transfer rate depended on the gluconic acid concentration. During the growth process, the oxygen transfer rate reached a value of about 13 g O₂ · kg^?1 · h^?1using a 30-l glass fermenter equipped with a 6 blade stirrer and fully baffled. This rate declined to a value of between 2 and 5 g O₂ · kg^?1 · h^?1 in the presence of gluconic acid concentrations above 150 g gluconic acid · kg^?1medium. The yield (g gluconic acid · g^?1glucose) depended on the gluconic acid concentration and amounted to y = 0.7 in relation to 150 g gluconic acid · kg^?1medium and y = 0.8 in relation to 200 g · kg^?1medium, respectively. The fermenters were coupled with ultrafiltration moduls (Fa. ROMICON and Fa. SARTORIUS). The biomass concentrations amounted from 5 to 40 g dry mass kg^?1medium. The ultrafiltration modules retained the biomass within the fermentation system. A glucose solution (30 to 50 weight percent glucose) was continuously dosed into the fermenter. The retention time was chosen between 2 and 30 h. The gluconic acid synthesis rate reached values of up to 32 g gluconic acid · kg^?1 · h^?1. Within a range of up to 250 g gluconic acid · kg^?1medium, the acid concentration had no influence on the enzyme activity.     

Inorganic carbon uptake by phytoplankton in Vineyard Sound,Massachusetts. II. Comparative primary productivity and nutritional status of winter and summer assemblages

Using time-course, natural-light incubations, we assessed the rate of carbon uptake at a range of light intensities, the effect of supplemental additions of nitrogen (as NH₄⁺ or urea) on light and dark carbon uptake, and the rates of uptake of NH₄⁺ and urea by phytoplankton from Vineyard Sound, Massachusetts from February through August 1982. During the winter, photoinhibition was severe, becoming manifested shortly after the start of an incubation, whereas during the summer, there was little to no evidence of photoinhibition during the first several hours after the start of an incubation. At light levels which were neither photoinhibiting nor light limiting, rates of carbon uptake normalized per liter were high and approximately equal during winter and summer (22–23 μg C·l^?1 · h^?1), and low during spring (<10 μgC·l^?1· h^?1). In contrast, on a chlorophyll a basis, rates of carbon fixation were as high during spring (15–20μg C·μg Chl a^?1·h^?1), when concentrations of chlorophyll a were at the yearly minimum (<0.5 μg · l^?1) as during the summer, when chlorophyll a concentrations were substantially higher (0.8–1.3 μg · l^?1). Highest rates of NH₄⁺ and urea uptake were observed during summer, and at no time of the year was there evidence for severe nitrogen deficiency, although moderate nitrogen nutritional stress was apparent during the summer months.     

FLOW‐INDUCED MORPHOLOGICAL VARIATIONS AFFECT DIFFUSION BOUNDARY‐LAYER THICKNESS OF MACROCYSTIS PYRIFERA (HETEROKONTOPHYTA,LAMINARIALES)1

In slow mainstream flows (<4–6 cm · s^?1), the transport of dissolved nutrients to seaweed blade surfaces is reduced due to the formation of thicker diffusion boundary layers (DBLs). The blade morphology of Macrocystis pyrifera (L.) C. Agardh varies with the hydrodynamic environment in which it grows; wave‐exposed blades are narrow and thick with small surface corrugations (1 mm tall), whereas wave‐sheltered blades are wider and thinner with large (2–5 cm) edge undulations. Within the surface corrugations of wave‐exposed blades, the DBL thickness, measured using an O₂ micro‐optode, ranged from 0.67 to 0.80 mm and did not vary with mainstream velocities between 0.8 and 4.5 cm · s^?1. At the corrugation apex, DBL thickness decreased with increasing seawater velocity, from 0.4 mm at 0.8 cm · s^?1 to being undetectable at 4.5 cm · s^?1. Results show how the wave‐exposed blades trap fluid within the corrugations at their surface. For wave‐sheltered blades at 0.8 cm · s^?1, a DBL thickness of 0.73 ± 0.31 mm within the edge undulation was 10‐fold greater than at the undulation apex, while at 2.1 cm · s^?1, DBL thicknesses were similar at <0.07 mm. Relative turbulence intensity was measured using an acoustic Doppler velocimeter (ADV), and overall, there was little evidence to support our hypothesis that the edge undulations of wave‐sheltered blades increased turbulence intensity compared to wave‐exposed blades. We discuss the positive and negative effects of thick DBLs at seaweed surfaces.     

EFFECTS OF ETHYLENE ON TETRASPOROGENESIS IN PTEROCLADIELLA CAPILLACEA (RHODOPHYTA)1

The effects of ethylene (C₂H₄) on tetrasporogenesis of the red seaweed Pterocladiella capillacea (S. G. Gmelin) Bornet were investigated. Ethylene is a gaseous hormone that is involved in a variety of physiological processes (e.g., flowering, fruit abscission) in higher plants. To study the effects of ethylene on the reproduction of the red seaweed P. capillacea, immature tetrasporophytic thalli were exposed to a flow of ethylene for different time periods. Maximum maturation of tetrasporangia was observed at 7 d in thalli exposed to ethylene for 15 min. This maturation was accompanied by a significant increase in the free fraction of putrescine (Put) and a 5‐fold increase in the level of total RNA. These changes were specifically due to ethylene since they were blocked by the presence of the ethylene perception inhibitor silver thiosulphate (STS). Moreover, P. capillacea was determined to produce ethylene at a rate of 1.12 ± 0.06 nmol ethylene · h^?1· g^?1 fresh weight (fwt) with specific activities for 1‐aminocyclopropane‐1‐acrylic acid (ACC) synthase of 11.21 ± 1.19 nmol ethylene · h^?1· mg^?1 protein and for ACC oxidase (ACO) of 7.12 ± 0.11 nmol ethylene · h^?1· mg^?1 protein. We conclude that ethylene may indeed be a physiological regulator of tetrasporogenesis in this red seaweed.     

IN SITU UPTAKE KINETICS OF AMMONIUM AND PHOSPHATE AND CHEMICAL COMPOSITION OF THE RED SEAWEED GRACILARIA TIKVAHIAE1

The uptake kinetics of ammonium and phosphate by Gracilaria tikvahiae McLachlan were studied under field conditions. Seaweeds, pulse fed once a week for 6 h over a 4-week period, had maximum uptake rates of 19 μmol·g fwt^?1·h^?1 for ammonium and 0.28 μmol·g fwt^?1·h^?1 for phosphate. For both nutrients there was a positive linear correlation between uptake rate (v) and concentration (S) over the entire range of concentration tested. In a nutrient depletion experiment, the phosphate uptake curve determined over a wide range of concentrations consisted of two stages of saturation at low concentrations, and a linear phase at high concentrations. Ash free dry weight, chlorophyll a, phycoerythrin, and protein content were higher in pulse fed plants than in control plants receiving no nutrient additions, while the reverse held true for carbohydrate contents and the C/N ratios. The C/N ratio inversely correlated with ammonium and phosphate uptake rate as well as protein and phycoerythrin content, and positively with carbohydrate content.     

PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P. “pseudolinearis” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance (P–I) curves revealed that maximal photosynthesis (P_max), irradiance at maximal photosynthesis (I_max), and compensation irradiance (I_c) varied with salinity, temperature, and species. The P_max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O₂ · g dwt^?1 · h^?1 (where dwt indicates dry weight) at 30–140 μmol photons · m^?2 · s^?1 (I_max) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m^?2·s^?1, and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P_max values but higher I_max values than those of P. abbottiae. The P_max of P. “pseudolinearis” conchocelis was 200–240 μmol O₂ · g dwt^?1 · h^?1 and for P. torta was 90–240 μmol O₂ · g dwt^?1 · h^?1. Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m^?2 · s^?1 at 30 psu, but P_max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m^?2 · s^?1, and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances (I_c) were relatively low (3–5 μmol · photons · m^?2 · s^?1) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.